Electronic elements for controlling temperature, limiting current, generating heat at constant temperature and like applications have employed a semiconducting ceramic having a positive temperature coefficient characteristic (hereinafter referred to as a PTC characteristic), wherein the electric resistance thereof drastically increases when temperature elevates beyond the Curie temperature. As such a semiconducting ceramic, barium titanate ceramics have widely been used.
In recent years, there has arisen demand for a semiconducting ceramic electronic element for the above applications which has a high withstand voltage (i.e., high withstanding voltage) and thus can be used at high voltage. Particularly, a semiconducting ceramic element employed in a overcurrent-protecting element for electric circuits must have high withstand voltage.
One known method which is effective for obtaining a semiconducting ceramic having high withstanding voltage is to reduce the particle size of the barium titanate powder serving as a starting material. Therefore, studies have been focused on methods for reducing the particle size. For example, Japanese Patent Publication (kokoku) No. 60-25004 discloses that a semiconducting ceramic having a grain size of 1-5 .mu.m and a maximum withstanding voltage of 500 V/mm is obtained by crushing and mixing barium titanate and Sb oxide serving as a semiconductivity-imparting agent; calcining under controlled conditions; compacting under controlled conditions; and firing the compact at 1350.degree. C.
However, conventional barium titanate and semiconducting ceramic thereof involve the following drawbacks 1 and 2.
1. In order to effectively reduce specific resistance at room temperature, the barium titanate powder is preferably fired at approximately 1300.degree. C. However, when the powder is fired at such a temperature, barium titanate grains grow to a size of approximately 1-5 .mu.m, to thereby fail to attain a target withstand voltage; and PA1 2. When the particle size of barium titanate powder decreases to 0.1 .mu.m or less, the specific resistance of the ceramic at room temperature tends to vary from product to product, and in some cases increases with time (i.e., undergoes changes over time).